linux-kernel - Re: [PATCH 0/3] drm: tinydrm driver for adafruit PiTFT 3.5" touchscreen

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Date:   Wed, 31 Oct 2018 17:27:57 +0100
From:   Noralf Trønnes <noralf@...nnes.org>
To:     Eric Anholt <eric@...olt.net>, dri-devel@...ts.freedesktop.org,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [PATCH 0/3] drm: tinydrm driver for adafruit PiTFT 3.5"
 touchscreen


Den 25.10.2018 18.29, skrev Eric Anholt:
> Eric Anholt <eric@...olt.net> writes:
>
>> I was going to start working on making the vc4 driver work with
>> tinydrm panels, but it turned out tinydrm didn't have the panel I had
>> previously bought.  So, last night I ported the fbtft staging
>> driver over to DRM.
>>
>> It seems to work (with DT at
>> https://github.com/anholt/linux/commits/drm-misc-next-hx8357d) --
>> fbdev works great including rotated, and so does modetest.  However,
>> when X11 comes up at 16bpp, I get:
>>
>> https://photos.app.goo.gl/8tuhzPFFoDGamEfk8
>>
>> If I have tinydrm set a preferred bpp of 24, X looks great.  Noralf,
>> any ideas?
> Also, with these patches and the format modifier patch I just sent, mesa
> with vc4 is now working with this driver on this branch:
>
> https://gitlab.freedesktop.org/anholt/mesa/commits/kmsro
>
> Now I wonder how we can improve performance of the SPI updates.

I just remembered that tinydrm does a full flush on page flips. And if
the dirtyfb ioctl is also used you end up with two flushes. This could
explain bad performance. I have been waiting for the dirtyfb through
atomic work to come to fruition, but nothing merged yet. That would give
dirty tracking on page flips.

Noralf.